I had a doubt so i tested it:
We are looking for the events in all of the inheritance tree. So if the extension adds a template event listener for prosilver, all styles which are inherited from prosilver will include this listener.

If it's placed in
all/ -> applies to every single style installed
prosilver/ -> applies to prosilver and any style which inherits from it
subsilver2/ -> applies to subsilver2 and any style which inherits from it
foobar/ -> applies to foobar and any style which inherits from it
barfoo/ -> applies to barfoo and any style which inherits from it
...
...
...

The most specific file is chosen, so if you have:
all/test.html
prosilver/test.html
foobar/test.html

With foobar inheriting from prosilver,

If the user uses prosilver, prosilver/test.html will be used; if the user uses foobar, foobar/test.html will be used; if the user uses subsilver, all/test.html will be used.

One does not rename folders right now with MODs so not sure when/why you would do that with Extensions.

Actually we do...

Currently, if I'm installing a mod and it has styles/prosilver/template/modfolder (and/or styles/prosilver/theme/modfolder). Then I have to (copy then) rename the prosilver folder to the name of the style that I'm using to ensure that the mod's style functions correctly on my board.

Ideally you should think of the style folders like this when writing an extension:

prosilver: this is for style files based on prosilver and will apply to prosilver and any prosilver based style.

subsilver2: this is for style files based on subsilver2 and will apply to subsilver2 and any subsilver2 inherited style.

all: This is for style files that would otherwise be duplicated if you were to supply them to prosilver and subsilver2. These would also be files that can be used in any style, in which it would not matter if the style was prosilver, subsilver2, or foobar.

I would like to ask if there is reason why "Extension management" is not on the top of "Customise" tab in ACP? While I'm not 100% sure I think users use it more often than "Style management".

Another thing is about translating of extensions. It seems that there in "Extension management" is a few untranslated information as "Extension name", "Description" and "Role" (in "Author Information"). I think it would be great (for users not for translators) if extensions authors put this information into language files.
I translated a few extensions (board announcements and board rules) and in language files I translated the name of extensions so it appears in my language on "Extensions" tab, but in English in "Style management". I think it would be more user friendly if at least "Extension name" is translated everywhere or, if there is some reason why it has to be in English, to make some kind of (translated) mouseover title for extension names.